1. Field of the Invention
The present invention relates to processes for making reduced gloss thermoplastic compositions, and more particularly relates to a process for producing reduced gloss thermoplastic compositions having improved impact strengths, gloss levels, and flammability ratings.
2. Description of the Related Art
Low gloss compositions comprising a polymer blend of a polycarbonate and an emulsion grafted ABS polymer, and a low gloss enhancing amount of a polyepoxide are known. See Jalbert et al. U.S. Pat. No. 5,026,777 which is incorporated herein by reference. A single step compounding process can result in undesired side reactions, including side reactions of the polyepoxide with additional ingredient such as phosphite stabilizers and some organic and metal pigments which may affect product consistency and quality. Also, in general, a single step compounding processes as set out in Jalbert exhibit consistency problems in obtaining consistent combinations of desired levels of low gloss and high impact strength, as well as other properties.
Attempts to overcome some of these problems include pending U.S. applications (1) Wildi et al., U.S. patent application Ser. No. 07/951600, filed Sep. 28, 1992, entitled Process Improvement for Improved Color Reduced Gloss Thermoplastic Compositions which involve compounding an acrylonitrile polymer with an electrophilic reagent to form polymeric gels and admixing an effective amount of water with the polymeric gels sufficient to reduce the yellowness index of the gels, and blending an effective gloss reducing amount of the reduced color gels with a thermoplastic resin; and (2) Wildi et al., U.S. patent application Ser. No. 07/841,141, filed Feb. 25, 1992, titled Reduced Gloss Thermoplastic Compositions and Processes for Making Thereof, which involves compounding an acrylonitrile polymer with an electrophilic reagent to form polymeric gels, and blending an effective gloss reducing amount of the gels with a thermoplastic resin. These prior U.S. applications set out solutions to some of the problems encountered in the single step process set out in Jalbert et al., U.S. Pat. No. 5,026,777, but a problem still exists in the inconsistency of producing a product having adequate physical properties such as surface gloss and impact strength.
Consequently, there is a need to provide a process which provides a consistent dispersion of the gels in the matrix resin, and thereby provides a consistently low gloss and consistently high impact strength in the final composition.